Introduction to Python

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In-Class Exercises, Session 8



PLEASE REFER to pythonreference.com for syntax to follow in coding these Exercises
 

FUNCTION ARGUMENTS AND RETURN VALUES
 
Ex. 8.1 Write a function that returns a value.

Define a demonstration function return_ten() that returns the value 10. 

def return_ten():

    # your function code here


val = return_ten()

print(val)          # 10
 
Ex. 8.2 Write a function with one argument and one return value.

Define function 'doubleme' that takes one argument, doubles the value, and returns the doubled value. Note: you must not use 'a' or 'b' inside the function, and you must not print inside the function -- value must be returned. 

# your function code here

a = 5
x = doubleme(a)
print(x)           # 10

b = 100
y = doubleme(b)
print(y)           # 200
 
Ex. 8.3 Write a function with two arguments and two return values.

Define function 'doubletwo' that takes two numeric arguments, doubles each of them, and returns the two doubled values. Note: you must not use 'a' or 'b' inside the function, and you must not print inside the function - values must be returned. 

# your function def here

a = 50
b = 10

c, d = doubletwo(a, b)

print(c)                # 100
print(d)                # 20
 
Ex. 8.4 Write a function that returns None, without explicitly returning it.

Write function greet(), which simply prints 'Hello, world!'. Printing x should show None. 

# make sure your function does not attempt to return anything



x = greet()
print(x)         # None
 
Ex. 8.5 Demonstration: remove a return statement and note the value.

The below function returns the sum of its arguments. First run the program and note the printed value, then remove the return statement to see the printed value. 

def get_sum(val1, val2):
    valsum = val1 + val2
    return valsum


r = get_sum(5, 10)
print(r)
 

LAB 1
 
Ex. 8.6 Write a function that returns a value.

Define function 'get_rand()' that uses the following code to generate a random number between 1 and 10, then returns that number. Note: you must not print inside the function -- value must be returned.

 
# code to place inside your function:
# randval = random.randint(1, 10)


import random

# your function code here



num = get_rand()

print(num)

If you see None printed, then you did not return anything from the function, but are printing the value returned from the function. Make sure not to print inside the function.
 
Ex. 8.7 Write a function with two arguments and one return value.

Define function get_sum() that takes two numeric arguments and returns the values summed. Note: you must not use 'x' or 'y' inside the function, and you must not print inside the function - value must be returned. 

# your function def here

x = 50
y = 25

z = get_sum(x, y)
print(z)           # 75
 
Ex. 8.8 Write a function with two arguments and one return value.

Define function get_prod() that takes two numeric arguments and returns their values multiplied together. 

# your function def here



aa = 5
bb = 9

c = get_prod(aa, bb)     # int, 45
print(c)                 # 45
 
Ex. 8.9 Write a function with one argument and one return value.

Define function get_upper() that takes a string argument and returns the value uppercased. 

# your function def here



x = 'hello'
y = get_upper(x)         # str, 'HELLO'

print(y)                 # HELLO
 
Ex. 8.10 Write a function with one argument and one return value.

Define function get_split() that takes a string argument for a comma-separated CSV string line and returns a list of values from the split. 

# your function def here



line = 'this,that,other'

items = get_split(line)        # list, ['this', 'that', 'other']

print(items)                   # ['this', 'that', 'other']
 
Ex. 8.11 Write a function with one argument and one return value.

Define function get_first_item() that takes a string argument for a comma-separated CSV string line and returns just the first comma-separated item from the line. 

# your function def here


line = '2017-09-03,Alpha Corp.'

first = get_first_item(line)      # str, '2017-09-03'

print(first)                      # 2017-09-03
 

TRAPPING EXCEPTIONS: TRY/EXCEPT
 
Ex. 8.12 Trap a "bad dict key" error. If the user's key can't be found in the dict, an error occurs -- test this by inputting a key of 'XXX'. Once you have observed the exception and exception type, use a 'try/except' statement to trap the exception and instead print 'key does not exist'. Make sure to put your 'try' block around just one line of code. 
z = {'a': 1, 'b': 2, 'c': 3}

ukey = input('please enter a key:  ')

print(z[ukey])
Sample program run: 
please enter a key:  XXX
key does not exist
 
Ex. 8.13 Trap a "bad list index" error. If the user's index can't be found in the list, an error occurs -- test this by inputting an index of 9. Once you have observed the exception and exception type, use a 'try/except' statement to trap the exception and instead print 'no value at that index'. Make sure to put your 'try' block around just one line of code. 
x = ['a', 'b', 'c', 'd']

uidx = int(input('please enter an index:  '))

print(x[uidx])
Sample program run: 
please enter an index:  9
no value at that index
 
Ex. 8.14 Trap a "bad int value" error. Add another except: block to the one below that will trap the exception that occurs if the user doesn't type a number. If this exception is trapped, print 'please enter a number'. 
x = ['a', 'b', 'c', 'd']

try:
    uidx = int(input('please enter an index:  '))
    print(x[uidx])
except IndexError:
    print('no value at that index')
Sample program run: 
please enter an index:  hey
please enter a number
 

SET COMPARISONS
 
Ex. 8.15 Show items in one set that are not in another set. Use set.difference(). 
xx = {'a', 'b', 'c', 'd'}
yy = {'b', 'd'}

# your code here
 
Ex. 8.16 Show items common between two sets. Use set.intersection(). 
xx = {'a', 'b', 'c', 'd'}
yy = {'c', 'd', 'e', 'f'}

# your code here
 
Ex. 8.17 Show all items that are in either of two sets. Use set.union(). 
xx = {'a', 'b', 'c', 'd'}
yy = {'c', 'd', 'e', 'f'}

# your code here
 

LIST COMPREHENSIONS
 
Ex. 8.18 Use a list comprehension to modify each item from a list.

The new list should have each value from the old list doubled. 

x = [1, 2, 3, 4]
Expected Output: 
[2, 4, 6, 8]
 
Ex. 8.19 Use a list comprehension to filter items from a list. The new list should have only those values that are greater than 100. 
temps = [86, 89, 93, 101, 92, 107, 90, 110]
Expected Output: 
[101, 107, 110]
 
Ex. 8.20 Use a list comprehension to both modify and filter items from a list. The new list should have each value above 0 doubled. 
aa = [-5, -3, 2, 0, 15, 73, -100]
Expected Output: 
[4, 30, 146]
 

LAB 2
 
Ex. 8.21 Show common items between two sets.

In a single statement, show what is common between the two sets. 

first_round = {'Miller, George', 'Adams, Abdul', 'Feiner, Billy', 'Pollinator, Jim'}

second_round = {'Adams, Abdul', 'Pollinator, Jim', 'Freeman, Kalley', 'Boom, Boom'}
Expected Output: 
{'Adams, Abdul', 'Pollinator, Jim'}

(Note that set results may be in any order.)
 
Ex. 8.22 Show difference between two sets.

In a single statement, show what is in set first_round that is not in set second_round; then show the reverse. 

first_round = {'Miller, George', 'Adams, Abdul', 'Feiner, Billy', 'Pollinator, Jim'}

second_round = {'Adams, Abdul', 'Pollinator, Jim', 'Freeman, Kalley', 'Boom, Boom'}
Expected Output: 
{'Miller, George', 'Feiner, Billy'}
{'Freeman, Kalley', 'Boom, Boom'}

(Note that set results may be in any order.)
 
Ex. 8.23 Show all values in two sets.

In a single statement, show a complete set of values contained in both sets. 

first_round = {'Miller, George', 'Adams, Abdul', 'Feiner, Billy', 'Pollinator, Jim'}

second_round = {'Adams, Abdul', 'Pollinator, Jim', 'Freeman, Kalley', 'Boom, Boom'}
Expected Output: 
{'Miller, George', 'Adams, Abdul', 'Feiner, Billy', 'Pollinator, Jim',
 'Freeman, Kalley', 'Boom, Boom'}

(Note that set results may be in any order.)
 
Ex. 8.24 Modify each item in a list using a list comprehension.

Write a list comprehension that uppercases each word in the list. Print the list. 

x = ["It's", 'important', 'to', 'speak', 'moderately.']
Expected Output: 
["IT'S", 'IMPORTANT', 'TO', 'SPEAK', 'MODERATELY.']
 
Ex. 8.25 Modify each item in a list using a list comprehension.

Write a list comprehension that returns the list of numbers showing their percentage value as a whole number (i.e., multiplied by 100). 

pcts = [.353, .4911, .0309, .9998]
Expected Output: 
[35.3, 49.11, 3.09, 99.98]
 
Ex. 8.26 Modify selected items in a list using a list comprehension.

Write a list comprehension that returns the square root of each number greater than 0. To calculate square root, you can raise to the power of 0.5, or num ** 0.5 (where num is the variable holding the number). 

x = [5, 3, -3, 9, -7, 0, 10]
Expected Output: 
[2.23606797749979, 1.7320508075688772, 3.0, 3.1622776601683795]

Note that there may be small fractional differences on your computer.
 
Ex. 8.27 Modify each item in a list using a list comprehension.

Write a list comprehension that returns a list of strings that show each number as a currency value with comma separators (use the f'${num:,} format string, where num is the variable holding the number). Also round each item to 2 decimal places. 

aa = [35392.7381, 100353.949, 98.2203, 1035392.9942]
Expected Output: 
['$35,392.74', '$100,353.95', '$98.22', '$1,035,392.99']
 

LIST COMPREHENSIONS: WORKING WITH FILES
 
Ex. 8.28 Use a list comprehension to strip each line of a file. Reading 'pyku.txt', use a list comprehension to generate a list of lines, each one stripped of the newline. Print the list as a whole - do not loop through it. 
fh = open('pyku.txt')

# your code here - resulting list of strings should
# be each line in 'pyku.txt' without newlines
 
Ex. 8.29 Use a list comprehension to derive information about each line of a file. Looping through 'pyku.txt', generate a new list with integers - the string length of each line in the file. Print the list. 
fh = open('pyku.txt')

# your code here

The resulting list of ints should be [20, 30, 30], assuming the lines have not been stripped or divided with splitlines()
 
Ex. 8.30 Use a list comprehension to extract a field from each row in a CSV file. Reading 'revenue.csv', use a list comprehension to generate a list of company names. Print the list as a whole. 
fh = open('revenue.csv')

# your code here

The resulting list of strings should be each company listed in 'revenue.csv'
 

LAB 3
 
Ex. 8.31 Select items from a list using a list comprehension.

Write a list comprehension that returns a list of lines that start with the year '2014' 

lines = [  '2014-03-09,Wilson,Joe,Acme Inc.',
           '2014-08-17,Fink,Bart,Beta LLC',
           '2018-09-03,Emerson,Will,Acme Inc.',
           '2020-12-09,Rodgers,Mary,Gamma Co.',
           '2014-07-01,Jones,Pete,Acme Inc.'
        ]
Expected Output: 
['2014-03-09,Wilson,Joe,Acme Inc.','2014-08-17,Fink,Bart,Beta LLC',
 '2014-07-01,Jones,Pete,Acme Inc.']
 
Ex. 8.32 Modify selected lines from a list using a list comprehension and a compound statement.

Write a list comprehension that returns a list of last names from each line. 

lines = [  '2014-03-09,Wilson,Joe,Acme Inc.',
           '2014-08-17,Fink,Bart,Beta LLC',
           '2018-09-03,Emerson,Will,Acme Inc.',
           '2020-12-09,Rodgers,Mary,Gamma Co.',
           '2014-07-01,Jones,Pete,Acme Inc.'
        ]
Expected Output: 
['Wilson', 'Fink', 'Emerson', 'Rodgers', 'Jones']
 
Ex. 8.33 Select lines from a list using a list comprehension and a compound statement.

Write a list comprehension that returns a list of only 'Acme Inc.' lines. 

lines = [  '2014-03-09,Wilson,Joe,Acme Inc.',
           '2014-08-17,Fink,Bart,Beta LLC',
           '2018-09-03,Emerson,Will,Acme Inc.',
           '2020-12-09,Rodgers,Mary,Gamma Co.',
           '2014-07-01,Jones,Pete,Acme Inc.'
        ]
Expected Output: 
['2014-03-09,Wilson,Joe,Acme Inc.','2018-09-03,Emerson,Will,Acme Inc.',
'2014-07-01,Jones,Pete,Acme Inc.']
 
Ex. 8.34 Modify selected lines from a list using a list comprehension and a compound statement.

Write a list comprehension that returns a list of last names only from 'Acme Inc.' lines. 

lines = [  '2014-03-09,Wilson,Joe,Acme Inc.',
           '2014-08-17,Fink,Bart,Beta LLC',
           '2018-09-03,Emerson,Will,Acme Inc.',
           '2020-12-09,Rodgers,Mary,Gamma Co.',
           '2014-07-01,Jones,Pete,Acme Inc.'
        ]
Expected Output: 
['Wilson', 'Emerson', 'Jones']
 
Ex. 8.35 Supreme Challenge!.

Write a list comprehension that returns the list of lines with only the last name uppercased. (Splitting the line, you can uppercase the first element, make a list out of it, append it to the list of remaining values, and use ','.join() with the list to reconstitute the comma-separated values.) 

lines = [  '2014-03-09,Wilson,Joe,Acme Inc.',
           '2014-08-17,Fink,Bart,Beta LLC',
           '2018-09-03,Emerson,Will,Acme Inc.',
           '2020-12-09,Rodgers,Mary,Gamma Co.',
           '2014-07-01,Jones,Pete,Acme Inc.'
        ]
Expected Output: 
['2014-03-09,WILSON,Joe,Acme Inc.', '2014-08-17,FINK,Bart,Beta LLC',
'2018-09-03,EMERSON,Will,Acme Inc.', '2020-12-09,RODGERS,Mary,Gamma Co.',
'2014-07-01,JONES,Pete,Acme Inc.']
 
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